If you want to protect against a police who at gun point would not allow you yourself to retrieve your phone from your pocket, but rather search you an take it

If you want to protect against a police who at gun point would not allow you yourself to retrieve your phone from your pocket, but rather search you an take it themselves, you should not use any biometric feature, be it FaceID or TouchID. They can force you to put your fingerprints on the phone. You should then just use a long and secure pin code, which they currently cannot obtain legally from you.